1. Field of the Invention
The present invention relates to a light/ozone asher and, more particularly, to a light/ozone asher in which a scum, that is, an organic residual generated after patterning of a resist or the like, is removed using UV rays and ozone. In addition, the present invention relates to a light ashing method and a manufacturing method of a semiconductor device.
2. Description of the Prior Art
FIGS. 15(a)-15(b) are a sectional view and a plan view illustrating a structure of a prior art light/ozone asher disclosed in "Semicon News p.47 No.12 ('88)".
In the figures, a light/ozone asher 201 includes a process chamber 220 in which resist and organic substances are removed. The process chamber 220 is a 200 to 250 mm square in plan view and 10 to 15 mm in height. A bottom 221a and a side wall 221b of the process chamber 220 are made of metal, such as aluminum, and an upper wall 222 of the chamber 220 is made of quartz which transmits UV rays. One end of an ozone introducing pipe 223 is open in the center of the upper wall 222.
In addition, UV lamps 202a and 202b and UV lamps 202c and 202d are disposed on the upper wall 222 of the process chamber 220 so as to be positioned on both sides of the ozone introducing pipe 223. A cross section of each of the UV lamps 202a to 202d is an oval configuration which is long sideways, from which UV rays are emitted in the vertical direction and hardly emitted in the horizontal direction. In addition, the UV lamp is approximately 200 mm in length, approximately 40 mm in width, and approximately 15 mm in thickness. The consumed power of each lamp is 140 W.
A sample stage 225 on which a sample 1 is put is disposed in the center of the process chamber 220, and the distance between the sample 1 on the sample stage 225 and each of the UV lamps 202a to 202d is 1 to 2 cm.
In addition, one end of a gas exhaust pipe 224 is open at an lower part of the center of the side wall 221b, which is perpendicular to the longitudinal side of the UV lamps 202a to 202d. In addition, the sample 1 comprises a substrate 10 and a resist film 11 formed on the substrate 10 and having an opening 11a.
Operation of the conventional light ozone asher will be described.
The sample 1 is put on the stage 225 in the process chamber 220, ozone (O.sub.3) is introduced into the process chamber 220 from the ozone introducing pipe 223, and the UV lamps 202a and 202d are lighted. Then, ozone (O.sub.3) introduced into the process chamber 220 through the ozone introducing pipe 223 absorbs UV rays having a wavelength of 254 nm from the UV lamps and separates to oxygen (O.sub.2) and active oxygen (O'). At this time, the resist film 11 absorbs UV rays having wavelengths of 254 nm and 185 nm from the UV lamps and changes in quality, whereby it is likely to react with active oxygen.
Then, the generated active oxygen is diffused to the sample 1 and reacts with the resist 11 and the organic substance (CnHm) on the sample, whereby the organic substance, such as the resist film, is decomposed into carbon monoxide (CO), carbon dioxide (CO.sub.2) and water vapor (H.sub.2 O) and removed. Then, the carbon monoxide, carbon dioxide, water vapor, oxygen, and ozone (O.sub.3) which was not decomposed are exhausted from the process chamber through the gas exhaust pipe 224.
Thus, since the light/ozone asher removes the resist film without using charged particles, damage to a base of the resist film is small when the resist film is removed as compared with a plasma asher.
However, although the damage to the base of the resist film is small when the organic substance, such as resist, is removed by the prior art light ozone asher, the light/ozone asher can not be used in a process of removing a scum, that is, an organic substance left where a resist is removed from the patterned resist film, in the manufacturing process of the semiconductor device because the sample surface is irradiated with UV rays.
Hereinafter, necessity of removing the scum in the manufacturing process of the semiconductor device and specific problems generated in the removal of the scum by the light/ozone asher will be described in detail.
There are process steps of patterning a semiconductor layer, an insulating layer, a metal layer, and the like by selective etching or lift-off in the manufacturing of a semiconductor device and, in the patterning steps, resist films having predetermined patterns are used as masks.
As shown in FIGS. 16(a)-16(e), a process of patterning an insulating film, a semiconductor film, or the like by selective wet-etching comprises forming a resist film 11 by applying, for example, a positive resist after a film 12 to be patterned is formed on the substrate (FIG. 16(a)), exposing the resist film 11 (FIG. 16(b)), removing a exposed part 11b of the resist film by development to form a resist opening 11a (FIG. 16(c)), selectively wet-etching the film 12 using the resist film 11 as a mask (FIG. 16(d)) and finally, removing the resist film 11 to complete the patterning of the film 12 (FIG. 16(e)).
However, when the resist film is developed, if the organic substance (development scum) 11c is left at the resist opening 11a, that is, at the part from which the resist is removed, the side surface of the opening of the film to be processed becomes uneven as shown in FIG. 16(d) or that film is not etched away in some cases. Meanwhile, the above-described defect in patterning is not generated in the case of dry etching even if there is left the development scum. However, if the pattern of the film formed by dry etching becomes fine, the same defect is generated as in wet etching.
In addition, as shown in FIGS. 17(a)-17(e), a process of patterning a metal film, such as an electrode material, by lift-off comprises forming a resist film 11 by applying, for example, a positive resist on the substrate 10 (FIG. 17(a)), exposing the resist film 11 (FIG. 17(b)), removing an exposed part 11b of the resist film by development to form a resist opening 11a (FIG. 17(c)), depositing a film material 13 on the whole surface by vapor deposition or the like (FIG. 17(d)) and lifting off the film material 13 through dissolution of the resist film 11 to form a film 13a having a predetermined pattern (FIG. 17(e)).
In case of the patterning by lift-off, when the resist film is developed, if the organic substance (development scum) 11c is left at the resist opening 11a, that is, at the part from which the resist is removed, the width of the film 13a patterned as shown in FIG. 17(e) varies according to position, or the film material is all removed in some cases.
Therefore, in the patterning process of the resist film, the above-described defect in the film caused by development scum has been conventionally prevented by removing the development scum in a plasma asher after the resist film is developed. In this case, however, the base layer of the resist film is considerably damaged by the plasma.
Thus, it is thought that the scum can be removed by a light ozone asher capable of removing an organic substance while preventing the damage to the base layer. However, when the light/ozone asher is used in removing the scum, a bad effect occurs in the resist film as follows because of UV rays.
That is, when the scum is removed by the light/ozone asher, the resist 11 changes in quality because of UV rays. For example, the positive resist becomes difficult to dissolve in a solvent such as acetone. More specifically, in the lift-off process, a solvent such as acetone permeates the resist film 11 from a corner A of the resist film 11 in which the film material 13 is thin as shown in FIG. 18(b), and the resist film is dissolved. At this time, however, if the resist film has changed in quality, the resist film is not dissolved by the solvent and it becomes difficult to lift off the film material.
In addition, since the sample 1 is heated by absorbing UV rays, the pattern configuration of the resist film 11 is destroyed as shown in FIG. 18(a), and it becomes very difficult to control the reduction of a resist film thickness below several nm even if the process is performed for a short time. Consequently, patterning precision of the film is considerably degraded.